Method of making a collagen membrane from porcine skin

ABSTRACT

Collagen membranes are formed from porcine rinds (i.e., pig skins) for us in a variety of applications and, most preferably, for wrapping food products, such as hams and the like. First, after removing skins from the porcine, the skins are promptly frozen. In later processing, the rinds are thawed and then enzymatically defatted. Then, a quick alkalinic hydrolyzation is performed on the rinds. Then, an acidic hydrolyzation is performed on the rinds. The rinds are then ground into a gel-like fluid mass. Finally, the fluid mass is extruded, sheeted and dried into a collagen membrane. The collagen membrane produced can be, in preferred embodiments, used for wrapping food products, such as hams.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the making of collagenmembranes and, more specifically, to the making of edible collagenmembranes for wrapping food products, such as hams and the like.

2. Description of the Related Art

Collagen membranes (a.k.a.: films, foils, etc.) are used in variety ofapplications, such as illustrated in U.S. Pat. Nos.: 5,736,180 (Spiceimpregnated edible wrapping foil); 5,520,925 (Material on the basis ofcollagen fibers for covering wounds); 5,190,810 (Composite for use inmaking protective articles for use in laser surgery); 5,103,816(Composite for use in making protective articles for use in lasersurgery); 5,028,695 (Process for the manufacture of collagen membranesused for hemostasis, the dressing of wounds and for implants); 4,131,650(Collagen foil for cosmetic application).

As illustrated in the above-listed '180 patent, some edible collagenfoils are known for, among other uses, wrapping food products, such ashams.

Collagen foils can be made from a variety of animal skins. However,making collagen foils from porcine skins (i.e., pig skins) presents anumber of unique problems over making such from, for example, cattle orbovine. For instance, problems result from the need to remove theporcine hair and to handle the high fat content of porcine skins.

Currently, there are some procedures for preparing collagen foils fromporcine skins, but these procedures are not satisfactory for thepreparation of food products and the like from the collagen foilproduced. The existing procedures focus on the preparation of theporcine skins for the creation of “leather” goods that are processed attanneries or the like.

Currently, collagen foils are prepared from porcine skins as set forthin paragraphs (a)-(c) below. The present invention is a greatadvancement over existing procedures. Specifically, existing proceduresutilize the following steps:

(a) Porcine skins are collected from an abattoir (i.e., an establishmentfor slaughtering) and are usually preserved with sodium chloride andsold via skin traders to tanneries (i.e, establishments for convertingskins into leather). At the tanneries, the goods are first washed withwater and wetting agents and, if necessary, enzymes are also used toremove adhering feces and sodium chloride. During additional steps, hairis removed from the skins using sodium sulfide and lime and, ifnecessary, using enzymes and lubricants. As a result, the skins (whichare alkalinic) are swollen to approximately 5-10 mm thick.

(b) To further process the skins into leather, the skins arehorizontally “split” into two layers. The lower layer, i.e., that whichis directed toward the animals's body, serves as the starting materialfor the manufacture of collagen foils. Depending upon the tannery, as anintermediate step, the material can often be stored for an indefiniteperiod in hygienically uncontrolled conditions.

(c) The “splits” are then subjected to a solution of caustic soda and/orlime in an alkalinic hydrolyzation process that can last for up to about15 days. Through the hydrolyzation process, the material becomesprepared for additional steps, particularly mincing. Due to themolecular characteristics of the bovine skin collagen used (reticularnetwork), hydrolyzation processes ranging from intense to aggressive arerequired. After the alkalinic hydrolyzation, the splits are brought to apH <3.5, after having first undergone a strong acidic treatment, e.g.,with hydrochloric acid, and then they are ground to a gel-like mass. Or,after alkalinic treatment, the skins are brought to a pH of 5-7 usingorganic or inorganic acids, ground to a fibrous pulp, and then broughtto a pH of <3.5. The fluid pulp, which contains less than 2.5% collagen,and to which other materials, such as glycerin, Karion® (sorbitol), andcross linking agents have been added, is extruded and dried in a banddryer to the foil.

The above-described procedures have significant disadvantages. Overall,the present inventors have found that the foregoing procedures are notsatisfactory for foodstuffs and the like. The present inventors havenoted that the foregoing procedures have, for example, the followingparticular disadvantages:

The preserving salts can have additives that should not appear in food.

The skins are not cleaned and are stored with fecal contamination.

The goods can be of questionable origin (i.e., in the trade of skins,there are also goods of questionable origin, such as, e.g., skins fromknackeries).

The processing in the tannery is based on the requirements for leatherproduction using technical chemicals.

The product is transported in a non-refrigerated state to the foilmanufacturers. As a result, in the warmer seasons, there is thepotential for increased bacterial contamination. This contamination caneven be substantial enough to cause partial putrefaction of the materialdelivered. The alkaline product can also potentially undergouncontrolled chemical decomposition, depending on the conditions oftemperature and the time interval between the splitting and the deliveryto the foil manufacturers.

The raw material for the foils is subjected to extreme deviations inquality due to the complex series of events that take place.

The aggressive alkalinic treatment (hydrolyzation) also leads todenaturing alterations in the collagen.

SUMMARY OF THE INVENTION

In view of the foregoing problems in the existing art, the presentinvention was created by the present inventors to overcome theabove-noted and other problems in the making of collagen membranes, andespecially in the making of edible collagen membranes made from porcineskins (a.k.a.: pig skins or pork rinds).

The present invention provides, among other things: a) a novel methodfor making a collagen membrane; b) a novel collagen membrane made by themethod; and c) a novel method of using the collagen membrane.

According to a first aspect of the invention, a method of making acollagen membrane from a porcine rind is provided which includes thesteps of: removing skins from the porcine and promptly freezing theremoved skins for processing; enzymatically defatting the rinds;performing a quick alkalinic hydrolyzation on the rinds; performing anacidic hydrolyzation on the rinds; grinding the rinds into a gel-likefluid mass; and extruding, sheeting and drying the gel-like mass into acollagen membrane.

According to another aspect of the invention, a collagen membrane ismade by the method of the first aspect of the invention. In onepreferred embodiment, the collagen membrane is wrapped around a foodproduct, such as a ham.

The above and other aspects, features and advantages of the inventionwill be further understood based on the following description of thepreferred embodiments in combination with the accompanying drawings andclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the accompanying drawings, in which like referencesindicate like parts, and in which:

FIG. 1 is a schematic diagram showing the finished foil on a product,such as a ham or other meat product.

DETAILED DESCRIPTION 0F THE PREFERRED EMBODIMENTS

As noted above, the present invention provides, among other things: a) anovel method for making a collagen membrane; b) a novel collagenmembrane made by the method; and c) a novel method of using the collagenmembrane.

The Method of Making the Product

The first aspect of the present invention involves a novel method ofmaking a collagen membrane (which may also be referred to as collagenfoil, film, etc.). In summary according to a first embodiment, themethod preferably includes the following general method steps (sequenceof the steps could change):

(a) collecting/freezing of the rinds

(b) defatting

(c) dehairing/alkalinic treatment

(d) acidic treatment

(e) forming into a gel-like mass

(f) extruding/drying

(a) Immediately after removing the porcine rinds at the abattoir (i.e.,promptly upon removing (e.g., skinning) the rinds from the hogs at theabattoir's establishment), the rinds are washed with cold or hot waterand dehaired. After this the rinds are promptly frozen for use as astarting material for the collagen membrane process. Preferably, therinds are quickly frozen while in a very clean condition and, thus,preserved for use. A variety of freezing techniques can be employed,such as, for example, subjecting the rinds to a −50° C. quick freezer orto a normal freezer at −18 to −28° C. It is also possible to subject therinds to dry ice or liquid nitrogen. It is also possible to start theprocess directly with fresh, unfrozen rinds.

Preferably, the rinds are maintained in such a frozen state until therinds are subsequently processed as discussed below. In this regard, thesubsequent processing steps are typically conducted at a differentlocation than the establishment of the abattoir and, thus, the rinds arealso preferably transported in this frozen state. For the subsequentprocessing in steps, step (b) et seq, discussed below, the frozen rindsshould preferably be thawed out to facilitate such processing;

(b) In the subsequent processing, the rinds are defatted in one or moresteps. this defatting is preferably carried out enzymatically with thehelp of wetting agents (e.g., detergents). Before starting the chemicalprocess, it is also possible to defatt the rinds mechanically (removingof fat over 15% of initial fat content). Also the defatting with waterand surfactant or with organic solvents is possible.

(c) Then the alkalinic treatment is performed with alkalinic reactingorganic or inorganic agents. This treatment could be combined with theremoval of the porcine bristles. Strong alkalinic reagents such assodium hydroxide or potassium hydroxide are able to dissolve thebristles and soften the collagen fiber structure. Also anorganic ororganic reducing agents like sulfides (e.g., sodium sulfide, potassiumsulfide) or thio compounds (e.g., thioalcoholes, thiourea, thioglycol)are able to dissolve the bristles.

(d) With acidic agents, the rinds are brought to a maximum pH of 4.0with inorganic (e.g., hydrochloric acid, sulfuric acid, phosphoric acid)or organic acids (e.g., lactic acid, citric acid, formic acid, aceticacid). During this treatment the rinds take up water (swell). This isimportant for the transformation of the rinds into a gel-like mass. Itis also possible to neutralize with acidic reacting agents to a pH 4-8,most preferably pH 5-7. The resulting deswollen material could be milledinto a fiber slurry. Later this slurry is acidified to pH <4 to get thegel like mass.

(e) The swollen rinds are ground into a gel-like mass. It is alsopossible to ground unswollen rinds at pH >4.0 into a collagen slurry andperform the acidification into the gel-like mass in a subsequentprocessing.

(f) Then the fluid mass is treated with known extrusion and drying stepsthat are analogous to those of prior art procedures utilized with bovineskins, as discussed herein and above.

The method of the present invention has substantial advantages over theexisting procedures. Some exemplary advantages include that:

1. Step (a) of the present method can advantageously

Provide a product that is appropriate for foodstuffs;

Provide a starting material for the films that has a consistently highquality;

Avoid raw material of non foodstuff sources;

Avoid burdening or contamination of the raw material with chemicals;

Avoid burdening or contamination of the raw material withmicrobiological contaminants;

Avoid uncontrolled chemical decomposition of the raw material; and

Avoid uncontrolled microbiological decomposition of the raw material.

(2) In step (b) through (e), both the high fat content as well as thecomparatively non-aggressive alkaline treatment can also preventdenaturating alterations in the collagen. Also moderate temperatures andnon-aggressive bleaching steps save the collagen. With such a resultingcollagen material it is possible to reduce or to avoid crosslinkingagents in the final product. In contrast, degraded collagen requires theuse of crosslinking agents to get the desired tensile strength.

The method according to the first aspect of the invention can include,in the following illustrative and non-limiting examples, features as setforth in greater detail as described herein and as schematically shownin the figures. The illustrative cases are based on exemplaryembodiments that have been produced.

In these exemplary embodiments, the treatment of the porcine skins afterthe above noted step (a) can include the specific procedural stepsdescribed below. ( In the following description, the percentages are inrelation to the weight of the rinds (i.e., the weight of the rinds=100%) and the “mixer” used was a stainless steel reaction vessel.)

EXAMPLE 1

Step 1: (Defatting)

In a first step (following collection and freezing), the very fattyrinds are defatted. This defatting step is preferably carried outenzymatically with the help of wetting agents (e.g., detergents).Preferably lipases are used to hydrolyze natural fat between thecollagen fibers. In addition, proteases are preferably used to supportthis action (i.e., to provide a more uniform defatting). In addition, asurfactant is preferably used to emulsify the released fatty acids. Thecombination of chemical and biochemical agents in this first step, andthe advantages therefrom, were not previously contemplated in the fieldof preparing edible foils or films.

In a specific non-limiting example, this defatting can be carried out asfollows (i.e., it should be understood that this is an exemplaryembodiment and can be varied by those in the art depending oncircumstances as appropriate (most preferable values in parenthesis):

Temperature: 10-35° C. (30° C.)

pH 7-11 (9-10)

(i) Place the following into the mixer Rinds 100% Water  50-150% (100%)Sodium carbonate 0-5% (3%) Fat dissolving enzymes (lipases) 0-2% (0.6%)Protein dissolving enzymes (proteases) 0-2% (0.5%) (ii) Treatment in themixer: 30 min-3 h (1 hour) (iii) Add to the above in the mixerSurfactant 0.05-3%   (0.5%) (iv) Treatment time in the mixer: 30 min-5 h(2 hours) (v) Rinse: Drain the water and dissolved chemicals from themixer (e.g., via a drain).

Step II: (Alkalinic Treatment/Dehairing (i.e., the removal of theporcine bristles)

In a second step, hair (e.g., roots within the skin) is removed from theporcine rinds. The presence of this hair is a problem particularly toporcine skins. In this “hair-removal” step, a combination of chemical,which preferably includes sodium sulfide, is used to dissolve thisundesired hair or bristle material. This step and the advantagestherefrom are also unknown in the field of edible foils. Normally thisdehairing step of bovine skin takes place in tanneries under technicalconditions. The use of the sulfide dehairing of porcine rinds underfoodstuff conditions is novel.

In a specific non-limiting example, this dehairing can be carried out asfollows (most preferable values in parenthesis):

Temperature: 10-35° C. (30° C.)

pH >9 (>12)

(i) Place in mixer: Lime 0.5-5% (3%) Water  20-50% (30%) Sodium sulfide  2-6% (4%) (ii) Treatment time in mixer:   2-8 h (5.5 hours) (iii) Addin mixer: Water rest to 100% (70%) (iv) Treatment time in mixer:   5-30min (10 minutes) (v) Rinse: Drain the water and dissolved chemicals fromthe mixer.

Alternatively, sodium sulfide other inorganic or organic reducing agentslike potassium sulfide or thio compounds e.g., thiolcoholes, thiourea,thioglycol are able to dissolve the bristles. The lime/reducing agentcould also be replaced by strong alkali e.g., sodium hydroxide orpotassium hydroxide alone, to remove the bristles.

Step III: (Washing)

Then, the porcine skins are preferably subjected to a washing step. In aspecific non-limiting example, the washing step can be carried out asfollows (most preferable values in parenthesis):

Temperature: 10-35° C. (30° C.)

(i) Place in mixer: Water 50-200% (100%) (ii) Treatment time in mixer: 5-30 min (10 minutes) (iii) Rinse: Drain the water and dissolvedchemicals from the mixer.

Step IV: (Cleaning and Opening Up)

In a subsequent preferred step, the rinds are cleaned, preferably withperoxide to bleach the rinds. Preferably, sodium hydroxide is used so asto provide an alkaline condition that is for better peroxide action.

The sodium hydroxide also “opens-up” the collagen structure—i.e.,provides the first step of collagen fiber separation. While sodiumhydroxide is used in prior art collagen processing, “opening-up” ofbovine rinds requires higher concentrations of sodium hydroxide andespecially longer time periods than with porcine rinds. The collagen ofbovine rinds is more crosslinked, and the material is harder and needs astronger hydrolyzation to “open-up” than does porcine rinds. Forexample, porcine rinds in the present invention can be processed with0.3-0.8% sodium hydroxide for 1-2 hours. Bovine rinds need 1-1.5% sodiumhydroxide for 12-24 hours or a lime suspension for at least 15 days.

In a specific non-limiting example, this step can be carried out asfollows (most preferable values in parenthesis):

Temperature: 10-35° (30° C.)

(i) Place in mixer: Water  50-200% (100%) Hydrogen peroxide (33-35%)  0-2% (1%) Sodium hydroxide 0.3-0.8% (0.6%) (ii) Treatment time inmixer:   1-2 h (1 hour) (iii) Rinse: Drain the water and dissolvedchemicals from the mixer.

Step V: (Further Washing)

The porcine skins are preferably then subjected to a further washingstep. In a specific non-limiting example, the further washing step canbe carried out as follows (most preferable values in parenthesis):

Temperature: 10-35° C. (30° C.)

(i) Place in mixer: Water 50-200% (100%) (ii) Treatment time in mixer: 5-40 min (20 minutes) (iii) Rinse: Drain the water and dissolvedchemicals from the mixer.

Step VI: (Acidification)

Following the above-described alkaline treatment and preferably at thispoint, a short acidic treatment is conducted. In this step, additionalopening-up is carried out—specifically, hydrolyzation of acid unstablecrosslinks takes place, dissolving acid soluble non-collagenous materialin the rinds.

In a specific non-limiting example, the acidification can be carried outas follows (most preferable values in parenthesis):

Temperature: 10-35° C. (30° C.)

pH max. 3.5

(i) Place in mixer: Water  30-150% (70%) Hydrochloric acid (31-33%)2.5-10% (7%) (iii) Treatment time in mixer:  15 min.-5 h (2 hours) (iv)Rinse: Drain the water and dissolved chemicals from the mixer.

Other possible acids: sulfuric acid, phosphoric acid or organic acids,e.g., lactic acid, citric acid, formic acid, acetic acid. Timeconsumption for this step: 15 minutes to 5 hours.

Step VII: (Additional Washing)

The porcine skins then are preferably subjected to an additional washingstep. In a specific non-limiting example, this washing step can becarried out as follows (most preferable values in parenthesis):

Temperature: 30° C.

(i) Place in mixer: Water 50-200% (100%) (ii) Treatment time in mixer: 5-40 min. (20 minutes) (iii) Rinse: Drain the water and dissolvedchemicals from the mixer.

(iv) Repeat steps (i) to (iii) until a pH of about 1.8-3.9 is achieved.In this manner, by increasing the pH, the collagen takes up water. Thus,the “water filled” material can be ground as follows directly into agel-like mass.

After this step, the washed rinds preferably have a pH of about 2.5 anda collagen content of about 13-21%.

Another way is a neutralization instead of acidification. The materialis ground into a collagen slurry which is then acidified into a gel-likemass (see Example 2).

Step VIII: (Grinding)

The washed rinds are preferably ground into a uniform gel-like mass.While grinding of skins to a gel-like mass is previously known incollagen processing, for improve grinding, the size is preferablyreduced in at least three stages. In this manner, the collagen fiber canbe much better protected than in comparison to the same size reductionusing only, e.g., two stages. Notably, only the small collagen particlemasses don't separate by the addition of water.

In a specific non-limiting example, the grinding step can be carried outas follows:

1. Dividing the rinds into approximately cubic centermeter pieces bymincing through plates with 10 mm holes or by chopping with blades.

2. Then, dividing the pieces into small pieces of approximately a fewmillimeter in diameter by mincing or pressing the material through aplate with 4 mm holes.

3. Then, grinding to <1 mm by pressing through <1 mm hole plates or withthe aid of a colloid mill or with the aid of a homogenizer.

During these procedures additional water or ice may be added.

Step IX: (Preparation of the Fluid Mass)

In a further step, the mass is preferably mixed with water and softener.A part of the water may be ice.

The softener includes for example dialcohols, trialcohols, polyalcohols,(e.g., glycerol) or polymer sugars (e.g., Sorbitol and Karion).

The collagen preparation procedure is very protective for the collagen.Therefore and importantly, the inventive collagen membrane normallyneeds no crosslinking agents for stabilization and improvement ofmechanical properties.

However, if desired, the following chemicals could act as crosslinkers:Organic crosslinkers, e.g., di-aldehydes, α-hydroxyaldehydes,di-isocyanates, bisacrylamides, acrolein, carbodimides, anhydrides,diene, polyene; and inorganic crosslinkers, e.g., aluminum compounds.For application in the mass, water soluble and slow reactive compounds(e.g., di-aldehydes, α-hydroxyaldhydes) are best. The water insolublefast reactive compounds should only be applied to the dry foil.

In one exemplary non-limiting case, the values of the fluid mass can beabout (most preferable values in parenthesis):

Collagen content: 1-25% (1.8%) Glycerol: 0-1% (0.5%) Sorbitol 0-1%(0.2%) pH: 2-3.6 (2.5%) Temperature: 3-18° C. (8° C.).

With respect to softening, it is noted that pure and dry collagen filmsare brittle. The step of softening creates collagen fiber separation toallow, e.g., fibers to easily change their positions with adjacentfibers. In this regard, water is about the best softener for collagen.The above mentioned softeners act indirectly—that is, they are veryhygroscopic and keep water in the collagen. However, these carbohydratesalso have a significant disadvantage—that is, they supportmicrobiological growth because they are a good available carbon source.

While fats are direct and good softeners, covering the dry collagen foilwith fats is not very effective. When that is done, the fats areincorporated only between the fibers and not inside the fibers. Addingfat-emulsions into the collagen mass achieves better results, but thisalso has two disadvantages:

1) emulsifying agents are present in the collagen foil; and

2) the fat can migrate to the surface of the collagen foil because it isnot fixed properly.

In preferred embodiments, non-removed natural fat is the best softener.This fat is well incorporated between and inside the fibers. Preferably,in the present method, the chemical process is adapted such that it doesnot remove all of the fat. The remaining fat, thus, is used as asoftener and only a small amount—or even no—additional carbohydratesoftener is needed. In comparison to other processes, the presentinvention is thus advantageous in working with fatty porcine rinds.

The removing of fat in the defatting step(s) depends on the:

temperature

pH

time

amount of lipase

amount of surfactant

amount of defatting steps

position in the process

Defatting is best done at a higher temperature (about 30° C.), at pH9-10, over extended time periods (up to e.g., 6 hours), with higheramounts of lipase (up to 1%), higher amounts of surfactant (up to 3%),more defatting steps (up to 5 or more over the whole procedure) andlater in the process, e.g., after the alkalinic treatment. The contentof non-removed fat can be in the range of 0-10%, (dry weight of thefoil).

With respect to crosslinking agents, it is noted that only naturalunaffected collagen shows the best mechanical properties. With prior artprocedures, high amounts of crosslinking agents are necessary after thenormally strong alkaline processes in the chemical treatment (i.e., thehydrolysis of the collagen molecules). The crosslinking agents are usedto synthetically reconstruct bigger molecules. With the present method,the collagen molecules can be protected and the amount of crosslinkingagents can be kept to a minimum.

Step XII: (Homogenization)

After the foregoing, a homogenization step is preferably performed.First, air bubbles are removed, then the slurry is passed to ahomogenizer, and then the material is pumped into stainless steelvessels.

A chemical importance of homogenization is that it facilitates theuniform distribution of the water. Homogenization is the final step ofreducing the size of collagen particles: fiber bundles and biggerparticles are divided into fibers and fibrils. Preferably, thehomogenization fulfills at least one, most preferably all, of thefollowing:

1) it does not affecting the fiber/fibril length;

2) it maximizes disintegration of fiber bundles into fibers/fibrils;and/or

3) it has a suitable fibers/fibrils relationship.

The above three points directly and strongly influence the mechanicalproperties of the collagen foil.

While disintegration steps are well known in collagen processing, thepresent method has not previously been contemplated by those in the art.The present invention can utilize a conventional homogenizer or acolloid mill. The homogenization step can be carried out with the samemachines as the grinding step described above. However, inhomogenization, the mass of material being homogenized has the finalcomposition (water content, collagen content, softener content, pH,temperature), where as the above-described grinding step is before thefinal adjusting of these parameters. Thus, during the homogenizationstep, the material is ground to less than 1 mm, for example by pressingthrough plates having holes less than 1 mm therein, or with the aide ofa colloid mill or homogenizer.

Step XIII: (Extrusion, Sheeting and Drying)

Then, the slurry preferably undergoes the steps of extrusion, sheetingand drying. In this regard, the slurry is preferably first directedthrough a slit extruder. The extruded slurry passing through theextruder is received on a conveyor belt. The slurry is preferablysheeted (e.g., with a sheeting roller). The extruded slurry is alsopreferably neutralized (e.g., directly thereafter the extruder).Neutralization is preferably performed with ammonium gas, or withsodiumhydrogencarbonate, or with other neutralization agents. It isnoted that prior to entering the extruder, the slurry has a pH of about2.0-3.6. At that pH level, the collagen particles are swollen (i.e.,they have a high water content). This high water content typically leadsto a deformation of the collagen on every level (e.g., molecules,microfibrils, elementary fibers, fibers). A direct drying of the slurrywithout neutralization can lead to a fixation of these deformations,such that the interaction of the collagen molecules is limited and thefoil strength is weakened. Thus, as per the foregoing, after extrusionand before drying, a fiber formation step is preferably performed. Thisfiber formation step can involve neutralization to higher pH values, asper the above, or a coagulation with high ionic strength solutions.

The chemicals used for this fiber formation and the time offered forfiber formation can influence the properties of the collagen foil.Ammonium gas, noted above, acts very quickly and, thus, may have somedisadvantages in good fiber formation. Sodiumhydrogencarbonate, alsonoted above, acts slowly, and, in consequence, the fiber formation andthe mechanical properties of the collagen foil can be improved. Prior tothe present invention, it was not previously contemplated to use ofsodiumhydrogencarbonate in this context in collagen processing.

The conveyor belt then preferably passes through a dryer. In the dryer,the neutralized slurry is preferably continuously air dried on the beltat about 60-90° C. Length of the dryer can be, as just one non-limitingexample, about 50 meters. The conveyor speed (e.g., the productionspeed) should be made to correspond to the length of the dryer. In onenon-limiting example, when the length of the dryer is about 50 meters,the conveyor speed (e.g., directly related to the output of the collagenfoil) can be about 3-9 meters per minute. Preferably, the crosswisewidth of the foil on the conveyor is up to about 60 cm (but, this sizecan be varied depending on circumstances).

The present invention for producing collagen film from porcine rindsdiffers substantially from the prior art, which utilizes dehaired bovinesplits having a very low fat content, collected from tanneries. Thus,the problems associated with the present invention, i.e., defatting ofthe very fatty material and removing of the bristles, are unknown in theprior art field of collagen film producers. The present collagen processprotects the collagen, therefore it is possible to produce the collagenfilm without crosslinking agents. The strong process used for bovinesplits weakens the material, then it is necessary to stabilize the foilwith crosslinking agents. To use no crosslinker is unknown in this art.Both the affected bovine collagen and the crosslinking leads to acollagen film with bad stretchability. On the other hand, highstretchability is an important quality criteria. Fat can improve thestretchability. For example, DE 196 40 019 A1 describes the addition offat into a mass to get a better stretchable collagen film. With thepresent invention, porcine fat in the porcine rinds leads to a collagenfoil with very good stretching properties.

Step XIV: (Storage)

Then, a final storage, e.g., packaging, step is performed. Prior topackaging, the collagen foil is preferably air-conditioned (dried).Before packaging, the humidity (moisture content) of the collagen filmshould be within the range of about 5-25%, more preferrably about10-20%, and most preferably between about 11-18% (the humidity level isrelated, for example, to the softening step and to the presentair-conditioning step). Among other things, this preferred humidityrange helps provide collagen foils that are better in use. In thisregard, humidity levels below about 15% can make the collagen films toobrittle, while humidity levels above about 20% can support excessmicrobiological growth. The product may have a thickness in the range ofabout 0.0-2mm, and a dry weight per square meter of about 10-50 g/m².

The Product and its Use

As discussed herein-above, the product (i.e., the collagen foil)produced by the process of the present invention has a number ofsubstantial advantages over existing collagen foils produced by theexisting procedures. These advantages can include, for example, that:

From the time of slaughtering, the microorganism count can be minimized,and there can be substantially no increase in the microorganism count.The present foil can be made free of pyrogens and other metabolicproducts of microorganisms.

The new foil can display a higher natural fat content. The foil can,thus, be less absorbent for water and also more elastic. The foil can,thus, require less—or even no—chemical emollients. In addition, thereduced water absorbency can improve the foil's malleability.

The product of the present invention can also have a better nativestructure. The foil can be more elastic as well as more stable, and canonly need minimal treatment—or even no treatment—with chemicalcross-linking agents.

The present product (due to the gentler manufacturing process) can havea higher isoelectric point, which reduces the aqueous uptake in theneutral range. The foil, thus, remains more stable and is moremalleable.

As described herein-above, the present product has substantial benefitsin applications where the collagen foil is used with food stuffs orwhere the requirements for such collagen foil are similar to that ofedible foils (e.g., where reduced contamination is desired). In the morepreferred embodiments, as shown in FIG. 1, the present foil F is used inmethods of wrapping food products P. Most preferably, the presentproduct is used in methods of wrapping meats and the like food products.In a very most preferred embodiment, the foil is used to wrap “hams.” Asnoted below, it should be understood by those in the art that thepresent invention has a variety of benefits and uses that are applicableto a wide range of applications.

Normally the collagen film leaves the dryer very brittle (because of thevery low water content). The fresh collagen film is difficult to handle.This very dry film shows a high affinity to water. The uptake of waterand humidity is fast and difficult to control. For the customer, thequickly water-absorbing collagen film is difficult to control. Collagenfilm not immediately used takes up a high amount of water in humid air.A sticky foil can be the result, which is very difficult to handle inthe machines. After some days, microbiological growth on the foil alsocan be a problem.

The incorporated residual natural fat makes the present product stableagainst variation of humidity. The collagen foil leaves the dryer withpreferably 11-13% residual water content. Even under humid airconditions this water content is stable and increases at most to astable maximum of about 15%.

The porcine collagen fibers are much thinner than the bovine fibers. Theresulting porcine foil is a much more compact woven material. Thispositively influences some important properties in the use as a wrap fore.g., oxygen permeability and the humidity permeability. The normaloxygen permeability is about 1000-2000 ml/m² d bar, whereas the presentinvention is in a range of 200-500. The normal humidity permeability isalso about 1000-2000 g/m² d bar, whereas the present invention is in arange of 100-300. With the present invention, non-smoked products arebetter protected against chemical oxidation and loss of water.

The present invention can be utilized for wrapping hams where a collagenfilm is transformed into a tube and the ham is placed inside the tube.Thereafter a net is wrapped around the ham. The present invention alsoacts as a barrier membrane to reduce the loss of water of cooked ham androast. The present invention also allows easy removal of the net.

The present invention can be utilized for the production of smoked ham,cooked salted meat articles, roast, scalded sausage, other sausages,fish products and pastry. The barrier membrane of the invention protectsagainst water loss, loss of fat, etc.

EXAMPLE 2

Step I: (Pretreatment)

In a first step the rinds are washed with a surfactant.

In a specific non-limiting example, this pretreatment can be carried outas follows (i.e., it should be understood that this is an exemplaryembodiment and can be varied by those in the art depending oncircumstances as appropriate (most preferable values in parenthesis):

Temperature: 10-25° C. (20° C.)

(i) Place the following into the mixer Rinds 100% Water  50-200% (100%)Surfactant 0.2-3% (1%) (ii) Treatment time in the mixer:  30 min.-4 h (1hour) (iii) Rinse: Drain the water and dissolved chemicals from themixer.

Step II: (Alklinic Treatment/Dehairing (i.e., the removal of the porcinebristles))

In a second step, hair (e.g., roots within the skin) is removed from theporcine rinds. The presence of this hair is a problem particular toporcine skins. In this “hair-removal” step, a combination of chemicals,which preferably includes sodium sulfide, is used to dissolve thisundesired hair or bristle materials. This step and the advantagestherefrom are also unknown in the prior art field of edible foils.Normally this dehairing step of bovine skins take place in tanneriesunder technical conditions. As noted above the use of the sulfidedehairing of porcine rinds under foodstuff conditions is novel.

In a specific non-limiting example, this dehairing can be carried out asfollows (most preferable values in parenthesis):

Temperature: 10-25° C. (20° C.)

pH >9 (>12)

(i) Place in mixer: Lime 0.5-5% (3%) Water  20-50% (30%) Sodium sulfide  2-6% (4%) (ii) Treatment time in mixer:   2-8 h (5 hours) (iii) Add inmixer: Water rest to 100% (70%) (iv) Treatment time in mixer:   5-30min. (10 minutes) (v) Rinse: Drain the water and dissolved chemicalsfrom the mixer.

Step III: (Washing)

Then, the porcine skins are preferably subjected to a washing step. In aspecific non-limiting example, the washing step can be carried out asfollows (most preferable values in parenthesis):

Temperature: 10-35° C. (30° C.)

(i) Place in mixer: Water 50-200% (100%) (ii) Treatment time in mixer: 5-30 min. (10 minutes) (iii) Rinse: Drain the water and dissolvechemical from the mixer.

Step IV: (Defatting)

In this defatting step the rinds are defatted. This defatting step ispreferably carried out enzymatically with the help of wetting agents(e.g., detergents). Preferably lipases are used to hydrolyze natural fatbetween the collagen fibers. In addition, proteases are preferably usedto support this action (i.e., to provide a more uniform defatting). Inaddition, a surfactant is preferably used to emulsify the released fattyacids. This first step, including the combination of chemicals andbiochemical agents therein, and the advantages therefrom were notpreviously contemplated in the field of preparing edible foils.

In a specific non-limiting example, this defatting can be carried out asfollows (i.e., it should be understood that this is an exemplaryembodiment and can be varied by those in the art depending oncircumstances as appropriate). (most preferable values in parenthesis):

Temperature: 10-35° C. (30° C.)

pH 8-13 (9-11)

(i) Place the following into the mixer Water   50-200% (100%) Fatdissolving enzymes (lipases)   0-2% (0.6%) (ii) Treatment time in themixer: 15 min.-6 h (1 hour) (iii) Add to the above in the mixer: Proteindissolving enzymes (proteases)   0-2% (0.5%) Surfactant 0.05-3% (0.5%)(iv) Treatment time in the mixer:   1-12 h (4 hour) (v) Rinse: Drain thewater and dissolved chemicals from the mixer.

Step V: (Further Washing)

Then, the porcine skins are preferably subjected to further washingstep. In as specific non-limiting example, the further washing step canbe carried out as follows (most preferable values in parenthesis):

Temperature: 10-35° C. (30° C.)

(i) Place in mixer: Water 50-200% (100%) (ii) Treatment time mixer: 5-40 min (20 minutes) (iii) Rinse: Drain the water and dissolvedchemicals from the mixer. (iv) Place in mixer: Water 50-200% (100%) (v)Treatment time in mixer:  5-40 min. (20 minutes) (vi) Rinse: Drain thewater and dissolved chemicals from the mixer.

Step VI: (Neutralization)

Then, following defatting, a neutralization is conducted. In this step,the rinds in a specific non-limiting example, the acidification can becarried out as follows (most preferable values in parenthesis):

Temperature: 10-35° C. (30° C.)

pH max. 3.5

(i) Place in mixer: Water  50-200% (100%) citric acid 0.5-2% (1%) (iii)Treatment time in mixer:   2-5 h (3 hours) (iv) Rinse: Drain the waterand dissolved chemicals from the mixer. (v) Place in mixer: Water 50-200% (100%) mono sodiumcitrate 0.5-5% (2%) (vi) Treatment time inmixer:   2-5 h (3 hours) Adjusting the pH with hydrochloric acid (10%):(vii) Add to the above in the mixer hydrochloric acid (10% 0.2-2% (1%)(viii) Treatment time in mixer  30 min.-5 h (2 hours) Repeat steps(vii)-(viii) until pH about 5 is reached (ix) The mixer stand over night(x) Rinse: Drain the water and dissolved chemicals from the mixer.

Step VII: (Additional Washing)

In a specific non-limiting example, the additional washing step can becarried out as follows (most preferable values in parenthesis):

Temperature: 10-35° C. (30° C.)

(i) Place in mixer: Water 50-200% (100%) (ii) Treatment time in mixer: 5-40 min. (20 minutes) (iii) Rinse: Drain the water and dissolvedchemicals from the mixer.

The material is ground into a collagen slurry which is then acidificatedinto a gel-like mass.

Step VIII (Grinding)

As in Example 1.

Step IX (Milling)

The ground material is mixed with 5 parts water and 3 parts ice. Millingin a colloid mill to a uniform collagen slurry.

Step X (Mass Preparation)

In a further step, the slurry is preferably mixed again with water, ice,hydrochloric acid and softener to a uniform gel-like mass.

In one exemplary non-limiting case, the values of the mixed mass can beabout:

Collagen content: 1-2.5% (1.8%) Glycerol 0-1.2% (0.6%) pH: 2-3.6 (2.8)Temperature: 3-18° C. (8° C.)

While the present invention has been shown and described with referenceto preferred embodiments presently contemplated as best modes forcarrying out the invention, it is understood that various changes may bemade in adapting the invention to different embodiments withoutdeparting from the broader inventive concepts disclosed herein andcomprehended by the claims which follow.

What is claimed is:
 1. A method of making a collagen membrane fromporcine rind material, consisting essentially of the steps: a) defattingporcine rind material to remove a majority of fat from the rindmaterial; b) chemically dehairing the rind material; c) performing anacidic hydrolization on the rind material; d) reducing the rind materialinto a gel-like mass of rind material containing collagen; and e)extruding, sheeting and drying the gel-like mass into a collagenmembrane, wherein steps a) to e) are performed without substantiallydenaturing said collagen so as to produce said collagen membrane.
 2. Themethod of claim 1, further including the step of removing skins from theporcine and freezing the removed skins to provide said rind materialprior to defatting.
 3. The method of claim 1 wherein the rinds areenzymatically defatted.
 4. The method of claim 1 wherein said rindmaterial is defatted so that the collagen membrane produced by themethod has a fat content of about 10% or less of a dry weight of thecollagen membrane.
 5. The method of claim 1 wherein said dehairing ofthe rind material is alkaline treatment of said rind material at ahair-removing pH.
 6. The method of claim 5 wherein after the dehairingstep, the rind material is washed.
 7. The method of claim 6 wherein,after the washing, the rind material is treated with a bleaching amountof peroxide and a collagen fiber-separating amount of sodium hydroxide.8. The method of claim 7, wherein after the treatment with peroxide andsodium hydroxide, the rind material is subjected to a further washingstep with water.
 9. The method of claim 7, wherein after the acidichydrolization of the rind material, the rind material is subjected to awashing step with water to achieve a pH of about 1.8-3.9.
 10. The methodof claim 1 wherein the rind material is reduced to a gel-like mass bygrinding.
 11. The method of claim 1 wherein the gel-like mass is mixedwith a membrane-softening amount of a softener selected from the groupconsisting of dialcohols, trialcohols, polyalcohols and polymer sugars.12. The method of claim 10 wherein, after grinding, the gel-like mass ishomogenized to provide substantially uniform distribution of water inthe mass and divide collagen in the mass into fibers and fibrils. 13.The method of claim 1 wherein the gel-like mass has a pH of about2.4-3.6 prior to extruding.
 14. The method of claim 1 wherein thecollagen membrane has a moisture content of about 11-18%.
 15. A collagenmembrane made by the method of claim
 1. 16. The method of claim 1wherein steps a) to e) are performed without addition of a softener toproduce said collagen membrane.